in the beginning he is thinking about how empty he feels now that he has lost his lover and friend. but then he begins to remember things that he forgot, "you were so bad/ falling, calling" he remembers the bad things about his ex and how they started to fall apart. at the time he may have been blind to it but in retrospect it becomes clear.

in the second stanza "now i'm getting closer there/ in the distance i hear friends" he is beginning to realize he doesn't have to stay empty forever. friends and family help the pain to slowly go away.
"maybe this keeps happening more" he is saying maybe i can feel happy more? he grows stronger and stronger and realizes "i can't see what i need you for" he doesn't need that relationship anymore.

"i was so young/ trying, trying" he was young (naive, foolish) and he kept trying to make it work but of course he couldn't.

"on the edge of my mistake" he is still recovering, still learning and growing from his mistake of losing his heart so quickly.
"so if i fuck this up again/ I dont know how i'll find the strength" he is saying that after this i can't let it happen again. finding the strength once is hard enough, he doesn't know if he would be able to do it again.

he closes his eyes, tries to go to sleep, but the thoughts still haunt him.
"I need light inside of me" the most beautiful line. He realizes that in order to be strong and overcome it fully he has to find the light within himself. Friends and family can only do so much, in the end we have look to ourselves and become our own hero.